Recent years have seen an evolution toward higher-power microprocessor, graphics, communication and memory semiconductor chips. This evolution in turn has driven interest in highly conductive solder thermal interface (STI) materials and liquid metal thermal interface (LMI) materials to provide improved thermal coupling between a chip and a heat sink. In both cases, it is an essential function of the thermal interface material that it thermally couple and adhere both to the chip and to the heat sink, in order to reduce the occurrence of failure in use (e.g., due to poor heat transfer between the chip and the heat sink).
A distinguishing feature of STI materials (which are understood to include low-melt solder materials that are solid at room temperature but may at least partially melt at normal chip process temperatures) is that they are composed of metal or metal alloys, such as gallium, indium, tin, lead or bismuth, among others. In some cases, these materials can attack or diffuse into other materials such as aluminum or copper, which are common heat sink materials. In other cases, these materials may fail to wet other materials such as silicon, silicon dioxide, silicon nitride or the like, which are common chip materials. De-wetting or degradation of the interface between the STI material and the heat sink, or between the STI material and the chip, can produce local hot spots that impede the thermal performance or cause outright failure of the chip in high-power applications. It is therefore desirable to provide a wetting or adhesion layer between a thermal interface material and a chip and/or between a thermal interface and a heat sink that maintains barrier properties and also isolates these mating surfaces from corrosive and adverse intermetallic formation with the interface metal.
Finally, both STI and LMI interfaces are conventionally applied in liquid phase. This requires the management of containment, void formation and intermetallic formations that are characteristic of liquid phase interactions. This is often difficult or impractical to achieve. Moreover, in cases where melting points exceed 125 degrees Celsius, attaching a heat sink would likely result in component failure.
Thus, there is a need for a metal thermal interface that provides good thermal coupling between a chip and a heat sink without the complicating need to enter liquid phase.